/**********************************************************************
 * Copyright (C) 2017-2017  Unisound
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 **********************************************************************
 *
 * Description : uni_md5sum.c
 * Author      : shangjinlong@unisound.com
 * Date        : 2019.05.14
 *
 **********************************************************************/
#include "uni_md5sum.h"
#include <string.h>

// Constants are the integer part of the sines of integers (in radians) * 2^32.
static const uint32_t k[64] = {
  0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
  0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
  0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
  0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
  0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
  0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
  0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
  0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
  0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
  0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
  0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,
  0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
  0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
  0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
  0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
  0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391};

// r specifies the per-round shift amounts
static const uint32_t r[] = {
  7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22,
  5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20,
  4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23,
  6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21};

// leftrotate function definition
#define LEFTROTATE(x, c) (((x) << (c)) | ((x) >> (32 - (c))))

static void to_bytes(uint32_t val, uint8_t *bytes) {
  bytes[0] = (uint8_t) val;
  bytes[1] = (uint8_t) (val >> 8);
  bytes[2] = (uint8_t) (val >> 16);
  bytes[3] = (uint8_t) (val >> 24);
}

static uint32_t to_int32(const uint8_t *bytes) {
  return (uint32_t) bytes[0] |
         ((uint32_t) bytes[1] << 8) |
         ((uint32_t) bytes[2] << 16) |
         ((uint32_t) bytes[3] << 24);
}

void Md5sum(const uint8_t *initial_msg, size_t initial_len,
            uint8_t digest[MD5SUM_LEN]) {
  // These vars will contain the hash
  uint32_t h0, h1, h2, h3;
  // Message (to prepare)
  uint8_t *msg = NULL;
  size_t new_len, offset;
  uint32_t w[16];
  uint32_t a, b, c, d, i, f, g, temp;
  // Initialize variables - simple count in nibbles:
  h0 = 0x67452301;
  h1 = 0xefcdab89;
  h2 = 0x98badcfe;
  h3 = 0x10325476;
  //Pre-processing:
  //append "1" bit to message
  //append "0" bits until message length in bits ≡ 448 (mod 512)
  //append length mod (2^64) to message
  for (new_len = initial_len + 1; new_len % (512 / 8) != 448 / 8; new_len++);
  msg = (uint8_t*)malloc(new_len + 8);
  memcpy(msg, initial_msg, initial_len);
  msg[initial_len] = 0x80; // append the "1" bit; most significant bit is "first"
  for (offset = initial_len + 1; offset < new_len; offset++) {
    msg[offset] = 0; // append "0" bits
  }
  // append the len in bits at the end of the buffer.
  to_bytes(initial_len * 8, msg + new_len);
  // initial_len>>29 == initial_len*8>>32, but avoids overflow.
  to_bytes(initial_len >> 29, msg + new_len + 4);
  // Process the message in successive 512-bit chunks:
  //for each 512-bit chunk of message:
  for(offset = 0; offset < new_len; offset += (512 / 8)) {
    // break chunk into sixteen 32-bit words w[j], 0 ≤ j ≤ 15
    for (i = 0; i < 16; i++) {
      w[i] = to_int32(msg + offset + i * 4);
    }
    // Initialize hash value for this chunk:
    a = h0;
    b = h1;
    c = h2;
    d = h3;
    // Main loop:
    for (i = 0; i < 64; i++) {
      if (i < 16) {
        f = (b & c) | ((~b) & d);
        g = i;
      } else if (i < 32) {
        f = (d & b) | ((~d) & c);
        g = (5 * i + 1) % 16;
      } else if (i < 48) {
        f = b ^ c ^ d;
        g = (3 * i + 5) % 16;
      } else {
        f = c ^ (b | (~d));
        g = (7 * i) % 16;
      }
      temp = d;
      d = c;
      c = b;
      b = b + LEFTROTATE((a + f + k[i] + w[g]), r[i]);
      a = temp;
    }
    // Add this chunk's hash to result so far:
    h0 += a;
    h1 += b;
    h2 += c;
    h3 += d;
  }
  // cleanup
  free(msg);
  //var char digest[16] := h0 append h1 append h2 append h3 //(Output is in little-endian)
  to_bytes(h0, digest);
  to_bytes(h1, digest + 4);
  to_bytes(h2, digest + 8);
  to_bytes(h3, digest + 12);
}
